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90 % viewer.


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hi all, another newbie question . my diagonal viewer on my celestron 90mm refractor ,is one that views objects right way up. so it has a prism to turn the image(so i believe anyway)

now would i get sharper views if i swapped this for a diagonal with just the mirror,and eliminate the prism. i was told more light will get through and therefore better images.

however,i will only do this if it is a big difference,due to the fact its new ,as am i. and dont want to risk breaking it. i only use scope for astronomy ,so upsidedown is no issue.

has anyone else got or had an astromaster 90mm celestron ?

thanks all,for any help to a newbie:icon_scratch:

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Hi rory, I don't think you would see much of a difference. Normal diagonals are supposed to have 99% reflectivity so a slight improvement on a prism, which do introduce chromatic aberrations on fast scopes, which you may have noticed.

Hope that helps

Handy little scope you have :glasses1:

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Hi Rory, When i bought my 70mm refractor it came with a 45 degree right way up jobbie and i bought a 90 degree star diagonal. I don't see much difference at all but it was worth it not to end up on my knees so often. Don't think you could break anything though, mine fits perfectly.

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okay ta. ive had suggested to me that the prism is losing me up to 10% light. i mean i can buy a standard mirror type, but dont really wanna spend dosh on that if id be better off using it to get a eyepiece of decent quality instead.

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It's a good question. I wouldn't think sharpness would be affected much, but i'd be interesed know if you can see fainter objects with a 99% dielectric diagonal compared to a 90% standard one, or if contrast would be improved. Has anyone had any experiences of this.

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Don't know if it's much help but I recently purchased a 2" gso dielectric diagonal to replace the standard 1 1/4" diagonal that came with my 6" f/8 frac. I'm more than certain that it is a definite improvement. Omega centauri has gone from a hazy ball with a few stellar points to one with a myriad stars across it's face. At higher mags the contrast has also improved. This was noted from my light polluted suburban location. Hope this helps.

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interesting. what im going to do ( if we ever get clear skies again!!!) take the diagonal off ,so there's no prism and use it like a traditional scope and see if the view is better. i know it will be upside down ect. but will be interesting to see the outcome. i tried it briefly in daylight at some tree's to see if i could focus ok. which i can .

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